The inventors have previously reported that a blood leucine rich alpha 2 glycoprotein (LRG) (hereinafter, also referred to as LRG) concentration can be used as a disease marker for inflammatory diseases such as ulcerative colitis, Crohn's disease, rheumatoid arthritis, Behcet's disease, and Castleman's disease, and LRG can be an excellent disease activity marker because LRG has a higher correlation with disease activity thereof than C-reactive proteins (hereinafter, also referred to as CRP), which have been used as in inflammation marker (Patent Literature 1, Non-patent Literatures 1 and 2).
However, the function of LRG in the above-described diseases has yet to be elucidated. It was completely unknown whether LRG can be a therapeutic target for inflammatory diseases such as ulcerative colitis and rheumatoid arthritis.